Johnny Depp has surprised fans by joining Aerosmith on stage during their Massachusetts gig.

The Pirates Of The Caribbean star, dressed in jeans and a black cap, strapped on his guitar to play Train Kept A Rollin' with Steven Tyler and his rocker bandmates at the Xfinity Centre in Mansfield, Massachusetts.

"He played guitar on the encore," a concert-goer told

His fiancee Amber Heard was reportedly watching the 51-year-old actor's musical performance from backstage.

Johnny's latest stage appearance came weeks after he accompanied Willie Nelson on guitar.

He previously rocked out with Aerosmith in August 2012, when he joined them during their Hollywood Bowl concert, and i n December 2012, he also performed Stop Messin' Around and Come Together with them during another show in LA.

Johnny is in Boston filming Black Mass, the biopic of gangster Whitey Bulger, which also stars Sienna Miller as Bulger's girlfriend Catherine Grieg.